Such shifting devices are known from DE 198 05 924 and DE 195 14 246.
In general, change-speed transmissions are used in motor vehicles in particular. They are used for the shifting, which is known to every car driver, of different speeds. This can take place either manually or automatically.
Change-speed transmissions for motor vehicles are generally arranged in the drive train between a clutch and axle gear assembly and transmit the engine torque and engine speed. The torque and speed are converted with the aid of pairs of gearwheels, of which one is generally a so-called idler gearwheel or shift gear which is connected in a rotationally fixed manner to its shaft. Differentiations are made in principle with respect to the components which connect the idler gearwheels to their shafts in a rotationally fixed manner, between synchronizer sleeve mechanisms and shift dog mechanisms. The power flux between the idler gearwheel and transmission shaft is established via a synchronizer sleeve which is connected in a rotationally fixed manner to the shaft via a synchronizing body. During a shifting process, respectively one synchronizer sleeve is displaced in such a manner that the corresponding idler gearwheel is connected in a rotationally fixed manner to the shaft. In that process, internal dogs of the synchronizer sleeve are pushed over a shifting toothing of the shifting speed.
The synchronizer sleeve is actuated with the aid of a (central) shifting shaft or shifting rod. For this purpose, “shifting fingers” which are operatively connected to the synchronizer sleeves are provided on the shifting shaft. The shifting shaft itself is usually actuated by means of a lever, as is customary in the case of lever-type speed change.
The shifting shaft is part of the change-speed transmission and is arranged in the housing thereof. The shifting shaft is displaced axially (shifting process) and/or rotated (changeover process) by means of the actuating element (transmission shifter).
In order to prevent two speeds of the (change-speed) transmission being selected or engaged simultaneously, i.e. to prevent the transmission of tensile force from the drive train to the output train taking place simultaneously via two different pairs of gearwheels, which would inevitably lead to the transmission being damaged or destroyed, so-called shifting gates are provided.
A shifting gate prevents incorrect shiftings and guarantees exact and comfortable shifting processes. The shifting travel, i.e. the possibilities as to the manner in which the shifting shaft can be moved, is limited, as far as an axial displacement (shifting) and rotation (changeover) are concerned. In the prior art, two different types of shifting gates are known.
A first shifting gate is shown in DE 198 05 924, which has already been mentioned above. In this case, a cup which is, for example, riveted to the shifting shaft is placed on to the end region of a central shifting shaft for limiting the shifting travel and for latching purposes (i.e. to retain the shifting shaft in a certain position for the purpose of maintenance and repair work). The cup has a wall in which a gate in the form of a recess is integrally formed in order to limit the shifting travel of the central shifting shaft.
A (positionally fixed) bolt can engage in this recess or gate. The bolt communicates with a transmission housing. The shifting shaft can be moved only in a manner permitted by the bolt engaging in the gate, i.e. the shifting shaft can be displaced axially or rotated only to such an extent that the gate which is fixed on the shaft (recess of the cup) strikes against the bolt.
DE 195 14 246 shows an alternative embodiment.
DE 195 14 246 likewise shows a shifting shaft which is mounted rotatably and displaceably in a known manner in a transmission housing and which transmits shifting and changeover movements fed in from an outer shifting mechanism, to a guiding pin. The guiding pin which is fixed on the shaft slides in slots (recesses) along the shifting gate, which is fixed on the housing. As a result, it can follow a predetermined shifting pattern. This enables axial and radial movements to also be transmitted to a shifting finger. The transmission can take place either directly to a shifting finger, which is connected to the shifting shaft, or through the shifting finger by means of a shifting arm which is actuated by a deflecting mechanism.
In this case, the shifting gate itself is connected in a positionally fixed manner to the transmission housing. The guiding pin is connected in a rotationally fixed manner to the shifting shaft, but can be displaced or rotated axially together with the shifting shaft. The outline or contour of the shifting gate forms a stopper for the guiding pin engaging in the shifting gate.
So that these components reliably carry out their task, high precision is required in their production. This makes the production of these parts very costly, since, for example, very complex contours have to be produced very precisely. Also the positioning of the shifting gate, as, for example, in the case of the transmission of DE 198 05 924 mentioned above, requires a high degree of accuracy. The positioning in the transmission housing itself has to be very precise and may result in complicated machinings being undertaken on the housing. These requirements in turn result in high costs.